The present invention relates to a slip factor learning method of a dual clutch transmission (DCT), and more particularly, to a slip factor learning method of a DCT, which is capable of controlling the DCT to perform gear shifting without a strange feeling, through a learning operation for a slip factor when torque transfer occurs between an off-going clutch and an on-going clutch in a gear shifting period of the DCT.
In general, a DCT includes two clutches unlike a conventional single-plate transmission system, and is connected to two input shafts and one output shaft. The input shaft is a rod-shaped shaft which transmits power to a position away therefrom through a rotary motion or linear reciprocating motion.
Furthermore, an engine is connected to the input shaft through a clutch, and the input shaft is connected to the output shaft through a gear and then transmits power to a wheel. The clutch used to couple or decouple shafts is a kind of shaft coupling device which temporarily disconnect or connect power of the engine, and is used when gear shifting is performed to change speed.
A general seven-speed DCT includes first and second input shafts and first and second clutches. The first input shaft is connected to odd-numbered gears (first, third, fifth, and seventh gears), and the first clutch connects a gear stage to the engine. The second input shaft is connected to a reverse gear and even-numbered gears (second, fourth, and sixth gears), and the second clutch connects a gear stage to the engine.
Thus, while the vehicle is operated in a state where the first clutch is connected to the output shaft through the first input shaft and an odd-numbered gear, gear shifting may be performed through a series of processes of applying even-numbered gear of the second input shaft, releasing the torque of the first clutch, and increasing the torque of the second clutch. At this time, the engaged (or coupled) clutch (for example, the second clutch) becomes an on-going clutch, and the other clutch (for example, the first clutch) of which the engagement is released (or disengaged) becomes an off-going clutch.
The DCT must accurately know the relation (TS curve) between clutch torque and stroke during clutch control, in order to reliably transmit an actually-inputted engine torque to a clutch. When a clutch torque equal to or more than a normal value is matched with a specific stroke on the TS curve, an excessive impact occurs. On the other hand, when a clutch torque less than the normal value is applied, the engine may be run up.
Furthermore, although the TS curve is accurately matched at the initial stage, the TS curve may be changed from actual situations, due to abrasion, thermal deformation, or mass-production deviation. Thus, the DCT learns the TS curve, in order to prevent an abnormality of the transmission system. However, although the DCT learns the TS curve, the friction characteristic or slip characteristic may be changed during a gear-shifting period in which a slip frequently occurs, which makes it difficult to perform gear shifting without a strange feeling. The slip may occur when coupling and releasing which are two frictional elements during gear shifting are not suitably controlled.
The related art of the present invention is disclosed in Korean Patent No. 10-1393762 published on May 2, 2014 and entitled “Method for estimating transmitted torque of dry-type clutch in vehicle”).